Acoustic design and adjustment are essential for various acoustic rooms including studios, listening booths, and halls.
When performing room acoustic design and adjustment in such various acoustic rooms, appropriate sound absorption and diffusion processing is first needed so as to avoid acoustic problems such as multiple reflections (flutter echoes) occurring between opposed wall surfaces in the room and long-path echoes of large delay time.
For that purpose, the proportions of sound absorption, reflection, and diffusion on the wall surfaces (sound field, acoustic environment) are adjusted and members are selected in order to provide desired acoustic characteristics (such as reverberation time) depending on the purposes and utilizations of the various acoustic rooms.
However, when wall surfaces in a small space of various acoustic rooms are covered with sound absorbing members to avoid the acoustic problems, the sound field can often have absorption characteristics of poor frequency balance, in particular, with excessive sound absorption in a high range and insufficient absorption to the low range.
The reason is that popular porous materials typified by glass wool, rock wool, and the like, which are the sound absorbing materials in common use, have the acoustic characteristics to absorb sound waves more in higher ranges and less in lower ranges. In fact, the acoustic characteristics of the porous materials can cause feelings unfavorable for the acoustic characteristics of a studio, including a “sense of confinement” and a “muffled feeling” due to excessive sound absorption level in a high range, and “obscurity” due to insufficient absorption level in a low range.
on the other hand, if the balance between sound absorption and reflection in a small space is adjusted by configuring the wall surfaces with conventional combinations of “sound absorbing surfaces” and “reflecting surfaces,” the reflecting surfaces or sound absorbing surfaces can exert an intense effect on certain locations and the sound field may be biased or vary greatly depending on the configuration and arrangement in a small space in particular.
Also, if the “sound absorbing surfaces” and “reflecting surfaces” are arranged regularly or periodically, particular reflection properties appear with periods corresponding to the arrangement pitch, causing “coloration” where certain frequencies are emphasized, or the like. Thus, it has been difficult to adjust for forming a sound field having well-balanced frequency characteristics.
As refer to Patent document 1, there is provided a sound absorbing layer which is arranged in front of a wall surface with respect to a sound source in a room and is made of a porous material for absorbing sound in the room. In addition, a diffusion layer of convex shape that diffuses sound passed through the absorption layer is arranged between the sound absorbing layer and the wall surface. The surface of the sound absorbing layer on the room side is formed in a convex diffusion shape for diffusing sound (hereinafter, referred to as conventional technology 1).
The sound absorbing structure of conventional technology 1 provides the effect of suppressing long-path echoes and flutter echoes of plane soundwaves in an architectural space by a considerable amount. A flutter echo refers to multiple reflections of soundwaves occurring in various acoustic rooms that are formed of reflective wall surfaces opposed in parallel. A long-path echo refers to reflected sound waves that are reflected by walls and the ceiling in a wide space and arrive with a time delay.